Heretofore, in the case of buildings, especially, high-rise buildings or large size buildings, expansion gaps are formed within the floor surface, wall surface or ceiling and the like of a building. Each gap is formed with a view to prevent breakage of the building by its absorption of any distortion as a result of expansion or contraction due to temperature changes within the building or irregular foundation support or distortion as a result of an earthquake and the like, and as a structure for covering the gap, the expansion joint shown in FIG. 8 has heretofore been used. The expansion joint of this kind is constructed in such a way that a cover plate 51 is fixed to a pair of support bases 50 fixed to ends of members A, A' of a building sandwiching a gap G, and in general, a connecting means 52 flexibly connects both support bases 50, 50 so as to span the gap G, and the cover plate 51 of the flat plate type is connected to the connecting means 52 by means of a bolt 53.
Accordingly, when the cover plate 51 was made of a metal plate, there was a problem that the design of the floor surface or wall surface or ceiling surface and the like of the building was divided by means of the cover plate 51 extending along the gap G. Especially, in recent years, as the width of the gap G is becoming larger as a result of a tendency of constructing larger size buildings, the width of the cover plate 51 is becoming correspondingly wider thereby producing a sense of design incompatibility in some cases.